Greenhouses are wonderful for extending the growing season in areas with long periods of cold for growing flowers that don’t typically flourish in an outdoor environment. The best greenhouse flowers include all types of orchids and lilies, biennials such as foxgloves, perennials such as lupine or delphinium and annuals of all sorts. In general, the best greenhouse flowers are those that appreciate a warm, humid environment.
There are a number of benefits that greenhouses provide to flowers that outdoor gardening does not. The environment is protected, so plants won’t be knocked over or damaged by high winds or scalding sunlight. The heat, even in an unheated greenhouse, is easier to regulate; as long as the greenhouse isn’t allowed to become too hot, the best greenhouse flowers will be those that prefer to set buds at a uniform temperature. Greenhouses also offer some protection again insects and many diseases. Flowers that are especially susceptible to white fly, voracious beetles, June bugs and other garden pests as well as diseases spread by these insects are a good choice to be grown in a greenhouse.
Among orchids, phalaenopsis, cattleya and ontoglossum orchids do especially well in regulated greenhouse environments. Odontoglossum prefer a cooler greenhouse. These beautiful orchids set buds in fragrant sprays and are happiest in a greenhouse where night time temperatures can be held at 55 degrees Fahrenheit (12.8 degrees Celsius) and daytime temperatures don’t rise above 75 degrees Fahrenheit (23.9 degrees Celsius). They thrive in filtered light and even humidity.
Cattleya orchids prefer intermediate temperatures between 60 degrees Fahrenheit (15.6 degrees Celsius) at night and 85 degrees Fahrenheit (29.4 degrees Celsius) during the day. Phalaenopsis orchids demand the most heat. They are intolerant of night temperatures below 65 degrees Fahrenheit (18.3 degrees Celsius) and will withstand a hot, humid environment of up to 90 degrees Fahrenheit (32.2 degree Celsius).
Calla lilies make excellent greenhouse flowers. Native to South America, their long, tube-like blossoms end in an open flute. They require shaded or filtered light and will become stressed by an overabundance of sunlight. It’s important for gardeners growing calla lilies to maintain even dampness in the soil and not permit it to dry out.
Biennial flowers such as foxgloves that normally require two years from planting to flowering are another excellent greenhouse choice. Gardeners can plant the seeds in the fall so that they have a garden-ready plant by spring for planting out. They might instead choose to keep the flowers in the greenhouse year-round, where they will often continue to set flowers for several years before burning out.
Perennial flowers such as delphiniums or lupines also make terrific greenhouse flowers. Lupines, which are from the pea family, produce blooms on tall stalks that can suffer from wind damage. They grow best in a cool greenhouse. Like lupines, the tall flowering stalks upon which delphinium blossoms grow are susceptible to strong wind and are especially delicious to many garden pests. The greenhouse environment can provide a protective year-round growing season or be used to prepare seedlings for planting out into protected outdoor areas.
All types of annuals get a head start as greenhouse flowers. By planting seeds in mid-winter, gardeners will have plants ready to burst into bloom when the time is right to plant them outdoors. Annuals that begin in greenhouses can range from impatiens to scabiosa.